Recent advances in computers and network-related technologies have been significant and multimedia information, which is a variety of information such as text, video and audio, is now being handled by computers and exchanged over networks. Since the amount of data involved in video and audio is comparatively large, processing is applied to encode and compress the data, thereby reducing the amount of data. By thus compressing image data and the like, more information can be transmitted to other devices at high speed via a network. The JPEG scheme, which compresses multivalued still images in compliance with ITU-T Recommendation T.81, is in wide use as an image compression technique. However, the standardization of JPEG 2000, etc., is being studied with a view to high-performance compression.
In the JPEG scheme, encoding that uses a discrete cosine transform (DCT) is fundamental. In JPEG 2000, a scheme that employs a discrete wavelet transform is effective.
FIGS. 7A and 7B are block diagrams illustrating the basic structures of a compression apparatus and an expansion apparatus, respectively. Specifically, as illustrated in FIG. 7A, an encoding apparatus compliant with ordinary JPEG and JPEG 2000 generally comprises a frequency transformation unit 701 for implementing a discrete cosine transform or discrete wavelet transform, a quantizer 702 and an entropy encoder 703, etc. On the other hand, as illustrated in FIG. 7B, an ordinary expansion apparatus compliant with JPEG or JPEG 2000 comprises an entropy decoder 704, a dequantizer 705 and an inverse frequency transformation unit 706, etc.
Since video or audio utilized by a computer or network is data that has been digitized, the environment thereof is such that the data can be reproduced with ease and the quality of the data is almost undiminished by such reproduction. For this reason, processing for embedding copyright information as a digital watermark in digital data such as images and voice is executed in order to protect the copyright of the digital data. By extracting the digital watermark from the digital data, it is possible to obtain the embedded copyright information to thereby discover and prevent the unauthorized reproduction of the data.
Known methods of embedding a digital watermark include a method utilizing a discrete cosine transform, a method utilizing a discrete Fourier transfer and a method utilizing a discrete wavelet transform, by way of example.
FIGS. 8A and 8B are block diagrams illustrating the basic structures of an ordinary digital watermark embedding apparatus and extracting apparatus, respectively. In general, as shown in FIG. 8A, the ordinary digital watermark embedding apparatus includes a frequency transformation unit 801 for implementing a discrete cosine transform or discrete wavelet transform, a digital watermark embedding unit 802 for performing quantization in accordance with information for embedding a frequency component, and an inverse frequency transformation unit 803, etc. On the other hand, as shown in FIG. 8B, the ordinary digital watermark extracting apparatus includes a frequency transformation unit 804, and a digital watermark extracting unit 805 for extracting embedded information from a quantized frequency component. Japanese Patent Application Laid-Open No. 2000-151411 (Patent Reference 1) and Japanese Patent Application Laid-Open No. 2000-151973 (Patent Reference 2) have been disclosed as examples of the prior art relating to this application.
In a case where image data is subjected to digital watermark embedding processing using the above described digital watermark embedding apparatus and to compression processing using the above-described compression apparatus, it is easy to apply the compression processing to the image data in which a digital watermark has been embedded. However, it is difficult to embed a digital watermark in compressed image data without expanding the data, apply compression processing again and output the result as image data.
FIG. 9 is a block diagram illustrating the basic structure of an information processing apparatus for subjecting compressed data to digital watermark embedding processing and compression processing. More specifically, as shown in FIG. 9, an image x is compressed by a frequency transformation unit 902, a quantizer 903 and an entropy encoder 904. This is followed by temporarily restoring the image data by applying expansion using an entropy decoder 905, a dequantizer 906 and an image inverse transformation unit 907. A digital watermark is then embedded by a frequency transformation unit 908, a digital watermark embedding unit 909 and an image inverse transformation unit 910. This output is compressed again by a frequency transformation unit 911, a quantizer 912 and an entropy encoder 913.
In accordance with FIG. 9, only processing by the frequency transformation unit 911, quantizer 912 and entropy encoder 913 will suffice in order to compress an image in which a digital watermark has been embedded. However, in order to embed a digital watermark in compressed data and compress the data again, the series of processing operations executed by the devices from the entropy decoder 905 to the entropy encoder 913 is required.
In actuality, many applications and devices that employ encoding processing such as JPEG encoding processing have already been put into practical use. Examples include devices such as digital cameras and color facsimile machines, still picture transmission systems and still picture processing systems. In these applications and devices, there are many cases where the processing by the frequency transformation unit 902, quantizer 903 and entropy encoder 904 is put into the form of hardware such as an ASICS, etc. Consequently, there is a significant rise in cost in order to additionally furnish such applications and devices, in which the above-described processing has been put into hardware form, with processing for embedding a digital watermark anew before compression and encoding.
Further, in JPEG 2000, the integration of compressive encoding and digital watermarking has not been studied sufficiently. Consequently, as in the case of the JPEG scheme, it is very likely that the aforementioned problem will arise, namely difficulty in embedding a digital watermark in compressed encoded data.